correlation between third molar size axial angulation, developmental stage and its relative position with possibility of mandibular second molar impaction in prospective possible impaction for lower second molars

Simultaneous formation of third molar crown with second molar eruption may possibly cause to second molar impaction due to third molar bud intervention. A tooth impaction leads to numerous clinical problems for the patient and the present study assessed the effect of third molar size, axis angulation, developmental stage and its bud position with possibility of mandibular second molar impaction in patients with doubtful impaction of lower second molars. In this descriptive-analytical study, 5420 records of 10-12 years old patients underwent orthodontic treatments in Tehran and Shahid Beheshti Dental Schools and private clinics were assessed and 38 patients [26 females and 12 males] were selected with possible impaction of lower second molars forming case group. 38 control patients with no prospective possibility for impaction of second molars were selected from the same centers and matched with the cases. The third molar axis angulation towards second molar, first molar and mandible base, mesiodistal width of wisdom teeth relative to second molar, Nolla developmental stage and third molar bud position regarding second molars were calculated and analyzed by student t, chi-square and mann-whitney U tests in both groups. The mean value of third molar angulation towards second molar, first molar and mandibular base were 24.16, 49.26 and 54.42 degrees in case group and 14.42, 39.39 and 45.0 degrees in control group respectively with significant differences [P<0.001 in three variables]. The mean mesiodistal width of third molar relative to second molar was 0.9903 in case Group and 0.9695 in control Group with no significant differences. Nolla developmental stage and marginal ridge of third molar bud towards second molar showed no definite effect on second molar impaction. The results suggest third molar angulation towards second molar, first molar and mandibular jaw base to be significantly higher in patients with possible mandibular second molar impaction than those without prospective possibility for second molar impaction. Although, no significant differences in mesiodistal width of third molar relative to second molars, developmental stage and marginal ridge of third molar bud regarding second molar were observed between the two groups

[Feasibility of recycling mechanical properties of used NiTi orthodontic wires by electromechanical treatment]

The desirable mechanical properties of nickel-titanium alloy wires have prompted many clinicians to recycle these wires. The purpose of this study was to investigate the changes in mechanical properties of nickel-titanium alloy wires after recycling by electromechanical treatment. In this experimental study, round 0.018 inch nickel-titanium wires [American Orthodontics trademark] were used. For purpose of determining the behavior of samples in mouth, the transformation temperatures of alloy were carried by electrical resistance test. The types of nickel-titanium wires were separated into three groups: 1- as received condition [control wires], 2- treated by low electrical current, 3- treated by high electrical current. Mechanical properties changes were observed by tensile testing. One-way analysis of variance and Tukey HSD [SPSS statistical package] was used for purpose of comparison. The results demonstrated significantly greater remained strains after recycling, but plateau stresses and elastic strain energies of the wires were decreased compared with the control wires. Super elastic property of electromechanical treated nickel-titanium wires is decreased following electromechanical treatments

[Prevalence of tongue tie in 12-14 year old students of Tehran, 2003]

Due to different complications of tongue tie, this study aimed at determining the prevalence of tongue tie in 12-14 year olds students of Tehran city in 2003. This descriptive study was done on 4900 students randomly selected and studied by questionnaire and clinical examinations. The examinations were done by dental mirror under daylight. The individuals who were unable to point the tongue tip or touch the palate with the tip of the tongue when the mouth was semi opened, were considered to be tongue tied. The data were analyzed by SPSS 11.0, descriptive statistics and chi-square test. Tongue tie prevalence was determined as 2.33% [114 cases]. 57[50%] of them were male and 57 ones [50%] were females. 67.6% of the patients showed crowding of upper anterior teeth, 30.7% crowding of lower anterior teeth, anterior and posterior crossbite was observed in 38.7% and 27% respectively, 6.3% and 17.1% presented anterior and posterior open bite, 17.1% with gingival recession in lower anterior teeth, 19.8% with diastema among lower central teeth. 41.4% had complaint from stiffness at shoulders, 20.7% from speaking disorders, 1.8% from breathing disorders and 28% of food impactions. 46.8%, 15.3% and 37.9% of them showed C1I, C1II and C1III respectively with no normal occlusion being found. The prevalence of tongue tie among Tehran students was higher compared to some studies. As different meanings are mentioned for tongue tie, this difference can be justified

[ effect ofpremolar extraction on lips' curvatures in borderline orthodontic patients]

Although orthodontists have long recognized that the extraction [Ext] of premolars often is accompanied by changes in the soft tissue profile, investigations indicate that the soft tissue does not always respond favorably to hard-tissue retraction. This study was designed to evaluate the effects of treatment, with and without premolar Ext. on the lateral facial profiles of borderline patients with particular reference to the curvature of the upper and lower lips. Eighty-nine border line patients were included in this study. 41 patients were treated with a non-extraction [Non-Ext] protocol, 16 patients were treated with extractions of 5/5, 18 patients with 4/4 and 14 patients with 4/5. All pre-and posttreatment lateral cephalograms were traced and analysis by one examiner. To quantify the soft tissue effects of growth and treatment, the depths of the upper and lower lip curves were calculated in two ways relative to the PM reference line and anterior soft tissue reference line.The changes in depth of upper and lower lip curves were statistically significant [P < 0.001]. The Non-Ext group showed an increase in depth of upper and lower lip curves, whereas the Ext group showed a decrease in depth of tipper and lower lip curves. No significant differences were found between the various extraction sequences [5/5. 4/4. 4/5] for depth of the upper and lower lip curves changes. The upper and lower lip changes were significant; more retrusivc in the Ext group and more protrusive in the Non-Ext group 2] There were no significant post treatment differences in the depths of upper and lower lip curves between premolar extraction sequences